The present invention relates to a process for the preparation of glycidylesters of branched monocarboxylic acids.
More in particular the present invention relates to a multistep process for the preparation of glycidylesters of xcex1-branched monocarboxylic acids containing from 5 to 20 carbon atoms and preferably from 9 to 13 carbon atoms.
Glycidylesters of xcex1-branched monocarboxylic acids are useful for the preparation of epoxy, acrylic polyester and alkyd resins, either directly or via intermediate products such as adducts with (meth)acrylic acid amines, polyols and polyacids or as reactive diluents for the preparation of thermoset acrylic, epoxy polyester and/or urethane paints and coatings.
Of particular interest are glycidylesters of aliphatic monocarboxylic acids represented by the formula 
wherein R1, R2 and R3 each represent the same or different alkyl radicals of normal or branched structure containing 1-20 carbon atoms, and R4 through R8 each represent hydrogen or a hydrocarbyl group containing 1-3 carbon atoms. A more preferred product is one where R1 through R3 are alkyl groups containing a sum total of 3-20 carbon atoms and where R4 through R8 are each hydrogen, e.g. the reaction product of neodecanoic acid (R1+R2+R3=C8) and epichlorohydrin.
Glycidylesters of this general type and their method of preparation are disclosed in U.S. Pat. Nos. 3,075,999, 3,178,454, 3,275,583 and 3,397,176, the complete disclosures of each of which are incorporated herein by reference.
Such glycidylesters can be made by reacting an alkali salt of the carboxylic acid with a halo-substituted monoepoxide such as an epihalohydrin, e.g., epichlorohydrin (1-20 molar excess). The mixture is heated (50-150xc2x0 C.) in the presence of a catalyst forming glycidylester plus alkali salt and water. The water and excess epihalohydrin are removed by azeotropic distillation, and the salt by-product, e.g., NaCl, is removed by filtration and/or washing. The glycidylesters can also be made by reacting the carboxylic acid directly with epichlorohydrin under similar process conditions. The chlorohydrin ester intermediate formed during this reaction is subsequently treated with an alkaline material, e.g., sodium or potassium hydroxide, which yields the desired glycidylester. By-product salt is removed by washing and/or filtration, and water is removed by drying.
Investigations of these reactions have revealed that several heavier by-products are produced during the reactions to varying degrees, and that species which add colour to the main product are contained within the heavier by-products. The heavier by-products include the reaction products of the glycidylester product and/or the chlorohydrin ester intermediate with either unreacted epichlorohydrin, unreacted monocarboxylic acid or salt and/or water at various stages of the synthesis process, and have been depicted hereinafter: 
The heavier by-products may also include further reaction products of initially formed compounds with the glycidylester product and other species present. Generally speaking, one or a combination of these or other unidentified heavies are present in the glycidylester reaction product at levels of from 8 wt % to 12 wt %.
Because glycidylesters are thermally and chemically reactive molecules, separation of these by-products from glycidylesters is not easily accomplished. Standard atmospheric distillation techniques have been found to increase the amount of by-products as well as the degree of colour of the esters. It is known that this increase in colour is caused by the reaction at elevated temperatures, as encountered during distillation, of the glycidyl functionality present in the desired product with functionalities present in the by-products, thereby forming additional by-products, which are not separable from the glycidylester and which are extremely sensitive to discoloration upon heating.
One of the remedies for solving this problem of said present by-products, has been disclosed in WO 97/44335.
In said application has been clearly suggested that standard vacuum distillation is ineffective in reducing the initial or aged colour of the glycidylesters and tends to worsen the colour problem.
In said patent application a process for the distillation of the glycidylester reaction product is proposed, which uses a thin film, short pass distillation apparatus and provides a light fraction which after recovery shows a Pt-Co colour value of less than 100 after 20 days storage in contact with air at 125xc2x0 C. when measured according to ASTM D1209.
Although said distillation process has provided glycidylesters of branched chain saturated monocarboxylic acids, showing an significantly reduced initial colour and a improved colour stability after periods of storage, it will be appreciated that such distillation process will cause a significant cost price increase of the final product, since the reported purity increases are only achieved by discarding about 8% of the intake for obtaining a 96% pure product and up to 30% of the intake for obtaining a 99% pure product. Moreover, said process leads to significant production of chlorinated waste, which is disadvantageous from an environmental point of view
It will be appreciated that there is still a need for an improved manufacturing process for glycidylesters of branched monocarboxylic acids, which may lead to the purity and/or colour performance of the product aimed at but at a lower cost price.
As object of the present invention therefor is to provide a process for the manufacture of glycidylesters of branched monocarboxylic acids, with improved initial colour, heat stability and colour stability and/or higher purity, which must be reached at a reduced cost price per product unit.
As a result of extensive research and experimentation, such a process has been surprisingly found now.
Accordingly, the invention relates to a process for the manufacture of glycidylesters of xcex1-branched monocarboxylic acids, comprising
(a) the reaction of the xcex1-branched monocarboxylic acid with a halo substituted monoepoxide such as an epihalohydrin (e.g. epichlorohydrin) in a 2-20 molar excess and preferably 3-20, optionally in the presence of water and water-miscible solvent and preferably an aqueous alkanol as solvent, and in the presence of a catalyst in an amount of at most 45 mol % of the molar amount of the monocarboxylic acid, and preferably at most 20% and more preferably of at most 10%, at a temperature in the range of from 30 to 110 (and preferably from 65 to 95xc2x0 C.), during a period in the range of from 0.5 to 2.5 hr,
(b) addition of additional alkali metal hydroxide or alkali metal alkanolate up to a total molar ratio as to the monocarboxylic acid in the range of from 0.9:1 to 1.2:1 and preferably from 0.95:1 to 1.10:1 and reaction at a temperature of from 0 to 80xc2x0 C. (and preferably from 20 to 70xc2x0 C.),
(c) distillation of the obtained reaction mixture to remove the excess halo substituted monoepoxide and the solvent and water formed, and
(d) removal of alkali metal halide salt, e.g. by washing the obtained glycidylester with water, after optionally treating the residual product with a concentrated aqueous alkali metal hydroxide solution, in order to complete the dehydrohalogenation (and preferably a dehydrochlorination).
It will be appreciated that the glycidylester obtained after step (d), can be dried in addition e.g. by distillation or treating with water absorbers.
The process according to the present invention can be carried out either as batch process or as a continuous process. The process preferably uses saturated xcex1-branched monocarboxylic acid.
The preferred reaction time in step (a) is in the range of from 0.9 to 1.5 hours.
The catalyst to be used in step (a) may be selected from alkalimetal hydroxides, alkalimetal carbonates, alkaline earth hydroxides, alkalimetal or alkaline earth metal alcoholates of the formula Xn+(ORxe2x88x92)n, wherein X represents the alkali metal or alkaline earth metal ion and R represents C1-C12 alkyl, n represents the valence of the metal ion, or
ammonium salts and in particular hydroxides or halides of the formula R1R2R3R4N⊕Yxe2x88x92, wherein R1, R2 and R3 independently of each other may represent an alkyl group having from 1 to 16 carbon atoms, which optionally may be substituted with one or more hydroxyl groups, wherein R4 represents an alkyl group having from 1 to 16 carbon atoms, phenyl or benzyl, and wherein Y represents hydroxyl or halogen.
Another suitable group of basic catalysts for step (a) is formed by phosphonium halides of the formula R5R6R7R8P⊕Zxe2x88x92, wherein R5, R6, R7 and R8 independent of each other may represent monovalent hydrocarbon groups. Preferably R5, R6 and R7 are alkyl, cycloalkyl, aryl, aralkyl, having at most 25 C-atoms and more preferably having at most 18 C-atoms, such as phenyl, butyl, octyl, lauryl, hexadecyl or cyclohexyl. R8 is preferably an alkyl group of from 1 to 10 C-atoms and more preferably of from 1 to 4 and wherein Z is a halogen, such as chlorine, bromine or iodine.
Alkalimetal hydroxides and alkali metal alkanolates having from 1 to 6 carbon atoms are most preferred as catalyst in step (a).
The alkalimetal hydroxide which is used in step (a) may be selected from sodium hydroxide, potassium hydroxide, lithium hydroxide, rubidium hydroxide, and cesium hydroxide, of which sodium hydroxide or potassium hydroxide is more preferred. It will be appreciated that in step (b) only relatively strong and water-soluble metal hydroxides or metal alcoholates have to be used, whereas weaker, less water-soluble metal hydroxides or carbonates are less preferred.
It will be appreciated that the specified molar ratios in step (b) will be constituted by additions of alkali metal hydroxides or alkali metal alkanoates on both steps (a) and (b).
With the term xe2x80x9cdistillationxe2x80x9d used in step (c) is meant removal of the light fractions from the initially obtained reaction mixture (which is indicated in the art as xe2x80x9ctoppingxe2x80x9d).
In addition, according to a preferred embodiment of the present invention the brine formed in step (a) can be completely or partially removed before entering step (b).
The alkali metal hydroxide or alkali metal alkanolate which is used in steps (b) and (d) are preferably selected from sodium hydroxide, sodium alkanolate having from 1 to 6 carbon atoms, such as sodium isopropanolate, lithium hydroxide or lithium alcoholate. Most preferably sodium hydroxide or sodium alkanolate having from 1 to 6 carbon atoms is used.
Preferably for step (b) sodium hydroxide is used in an aqueous solution of a concentration of from 15 to 60% by weight and more preferably from 20 to 50% by weight.
It will be appreciated that according to the process of the present invention a drying step can take place after the washing in step (d), if desired.
Usually mixtures of glycidylesters of branched monocarboxylic acids are produced, when starting from technical grades of commercially available compositions of xcex1-branched monocarboxylic isomers, such as neodecanoic acids, 2-ethyl hexanoic acid or VERSATIC 9 or 10 or 13 acids (VERSATIC is a trademark) as starting materials.
Preferably VERSATIC acids having 9 to 11 carbon atoms are used as starting material.
It will be appreciated that according to the more preferred embodiments of the process of the present invention step (d) will be carried as anhydrous as possible, i.e. using highly concentrated sodium hydroxide solutions e.g. up to 55 wt %.
It has surprisingly been found, that the process of the present invention can provide very pure glycidylesters of branched monocarboxylic acid, i.e. showing contents of heavier byproducts less than 6 wt % and preferably less than 5 wt % and more preferably less than 4 wt %, which show the desired reduced initial colour, the improved colour stability after periods of storage, and which do not need tailing by distillation for purification, while the process can be further characterized by a very high conversion and selectivity of the halo substituted epoxide with reference to the desired glycidylester.
More in particular it could not be expected by a person skilled in the art that the presence of a base in steps (b) and (d) does not significantly hydrolize the present, just formed glycidylester.
It will be appreciated that preferably an alkanol will be used which enables the dissolution of a sufficient amount of base into the organic phase, whereas on the other hand the total water content in the reaction mixture of step (a) is to be kept in the range of from 4 to 13 mol/mol acid.
With the term xe2x80x9calkanolxe2x80x9d as used throughout this specification is meant mono-alkanol as well as polyalkanols such as glycols.
Isopropylalcohol has been found to be most preferred.
The process of the present invention is more preferably carried out, starting from VERSATIC acids, containing from 5 to 13 carbon atoms, and most preferably from 9 to 11 carbon atoms.
It has been found that the water content in step (d) should be as low as possible to avoid hydrolysis of the glycidylesters to be formed. Preferably a highly concentrated aqueous solution of alkali metal hydroxide is used in step (d).
For the same reason the hydrolysable chlorine content after step (b) should be minimized ( less than 2500 mg/kg). A too high level can be reduced by known methods such as an increase of the amount of base used or by a reduction of the reaction temperature in step (b).
The following examples and comparative examples are illustrative of the invention, however without restricting its scope to this embodiment.